Re: [PATCH v2] PCI: pciehp: Avoid dropping hotplug interrupts due to stale HPIE

[sashiko-bot@kernel.org]

> pciehp_isr() uses the Hot-Plug Interrupt Enable (HPIE) bit in
> ctrl->slot_ctrl to reject interrupts when hotplug interrupts are
> disabled.  This check is needed because hotplug can share an interrupt
> with other sources, including native PME.
> 
> However, ctrl->slot_ctrl is updated from hardware on every Slot Control
> Register read-modify-write.  A firmware change to HPIE can race with an
> unrelated driver operation, such as an LED indicator update:
> 
>   1. The driver enables hotplug interrupts, setting both hardware HPIE
> 	  and the cached HPIE bit to 1.
>   2. Firmware temporarily clears hardware HPIE; the cached bit remains 1.
>   3. pcie_do_write_cmd() reads Slot Control for an indicator update and
> 	  observes HPIE=0.  Since the command's mask excludes HPIE, it
> 	  preserves the value read from hardware.
> [ ... ]
> This prevents stale-cache rejection of delivered interrupts, but does
> not restore hardware interrupt delivery.  If firmware restores HPIE
> before the driver's write, that write may clear it again.
> 
> Signed-off-by: Zhu Qiyu <qiyuzhu2@amd.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260925114635.192878-1-qiyuzhu2@amd.com?part=1